The specific aims for the next three years of the proposed project are: 1. To study the electrophysiologic response of nerves which supply the facet joint capsule of the rabbit lumbar spine. Mechanical stimuli resulting from deformations due to spinal loading will be used to elicit this response. Capsular strains will be measured simultaneously. Morphological studies of the nerves innervating the facet joint will be performed to support the electrophysiological studies. 2. To determine the strain in the cadaveric lumbar facet joint capsule which is richly innervated with sensory nerve endings. A variety of loading conditions, such as axial compression, flexion, extension, lateral bending, and twisting will be used, individually and in combinations. Finite element modelling will provide a more complete picture of the strain distribution in the capsule. The theme of this study is the correlation of electrical activities of nerve endings to mechanical loading of the spine. The specific aims are based on the hypothesis that idiopathic low back pain (LBP), not involving nerve root compression due to bony hypertrophy and/or disc bulge or rupture, is caused by the mechanical deformation of the facet joint capsule, which is richly innervated with sensory nerve endings. This interdisciplinary study will attempt to identify a probable cause of LBP not related to nerve root compression. Results from our biomechanical and electro-physiological testing of the lumbar facet capsule have shown that the human cadaveric capsule undergoes large deformations during facet loading and that there is neuronal activity in capsules of rats when the capsules are stimulated mechanically. Our recent immunocytochemical studies have shown that the facet joint of the rabbit contains a significant population of nerve fibers containing substance P which is a neuropeptide thought to play a major role in the transmission of pain.